Method and apparatus for reducing sonic booms

ABSTRACT

The sonic boom produced by a supersonic aircraft is attenuated by producing an expansion wave which interacts with the boomproducing shock wave as it travels toward the ground.

United States Patent Alperin [151 3,647,160 [451 Mar. 7, 1972 [54] METHOD AND APPARATUS FOR REDUCING SONIC BOOMS [72] Inventor: Morton Alperin, 6000 Lockhurst Drive,

Woodland Hills, Calif. 91364 [22] Filed: Sept. 23, 1968 [21] Appl.No.: 761,592

Related U.S. Application Data [63] Continuation-impart of Ser. No. 741,162, June 28,

1968, abandoned.

[52] U.S. Cl. ..244/1 N [51] Int. Cl ..B64c 23/04 [58] Field of Search ..244/1, 130, 35-36, 244/41 [56] References Cited UNITED STATES PATENTS 3,391,884 7/1968 Carbartt... ....244/45 X 2,916,230 12/1959 Nial "244/35 X 3,314,629 4/ 1967 Rethorst ..244/35 OTHER PUBLICATIONS H. L. Runyan and H. R. Henderson; Evaluation of Certain Minimum Boom Concepts Published in Proceedings of Second Conference on Sonic Boom Research edited by D. R. Schwartz; NASA SP-180; Washington, D. C., May 9-10, 1968; PP- 7- S1 Moeckel, W. E.; Theoretical Aerodynamics Coefficients of Two-Dimensional Supersonic Biplanes; NACA Technical Note No. 1316; June 1947 Primary ExaminerMilton Buchler Assistant Examiner-J. L. Forman Attorney-Christie, Parker & Hale ABSTRACT The sonic boom produced by a supersonic aircraft is attenuated by producing an expansion wave which interacts with the boom-producing shock wave as it travels toward the ground.

8 Claims, 1 1 Drawing Figures PATENTEUMAR 7 m2 SHEET 2 [IF 4 METHOD AND APPARATUS FOR REDUCING SONIC BOOMS This application is a continuation-in-part of my earlier filed application bearing Ser. No. 741,162 and filed on June 28, 1968, now abandoned, and entitled METHOD AND AP- PARATUS FOR REDUCING SONIC BOOMS.

The present invention relates to aerodynamic structures and in'particular to methods and apparatus for reducing sonic booms due to the motion of objects through the atmosphere at speeds greater than the speed of sound.

At the present time, supersonic aircraft and missiles can move in the atmosphere at speeds greater than the speed of sound. Generally, these conventional objects or vehicles have some sort of airfoil structure or wing extending outside for the production of lift to balance their gravitational attraction towards earth. When these aerodynamic structures move at speeds greater than the speed of sound in the surrounding fluid, local increases in pressure are developed as a result of the airflow beneath the lifting surface, leading to the formation of shock waves which produce an aerodynamic sonic boom at ground level. These sonic booms reveal the presence of the vehicle although it may not be visible by the naked eye at ground level. In addition, the shock wave created by these sonic booms are very annoying to humans and animals, and can cause substantial physical damage, particularly when they occur in residential or industrial areas. These sonic booms have resulted in awakened babies, frightened animals and shattered windows, for example. With the introduction of the supersonic transports, it is predicted that the sonic boom will cover a 50-mile wide corridor. For these reasons, then, it would be essential to minimize or eliminate the sonic boom. Existing supersonic aircraft cannot avoid the sonic boom or even reduce its magnitude to acceptable levels.

The present invention provides an improved method for reducing sonic booms created by objects moving in fluids at speeds greater than the speed of sound. The supersonic object usually has a primary lifting surface extending therefrom, and in travelling at supersonic speeds this surface or wing causes increases in local pressures leading to the formation of shock waves and therefore audible sonic booms at all altitudes from the object to the ground. The method of the present invention includes the step of diverting the airflow from its direction of v motion induced by the conventional primary wing to produce anexpansion wave in the immediate vicinity of the compression' or shock wave of the primary surface which interacts with this shock wave and causes it to be attenuated rapidly and become tolerable at ground level. The method includes the modification of the conventional lifting surface-geometry to produce an expansion wave in the immediate vicinity of the shock wave emanating from the primary lifting surface.

The method further comprehends the provision of a modified primary airfoil having a lower surface causing a plurality of expansion and shock waves to be produced for interaction whereby the shock waves are attenuated to render them tolerable at ground level.

From the structural standpoint, the invention comprehends a conventional aerodynamic structure such as a supersonic aircraft having a primary airfoil, the airflow beneath the primary airfoil assuming a parallel relationship therewith and causing an increase in local pressures leading to the formation of shock waves and thereby sonic booms. The aerodynamic structure includes an ordinary airfoil mounted thereto; below, and in a nonparallel relationship with the primary airfoil an auxiliary surface is properly arranged for diverting the airflow from a parallel relationship with the primary airfoil, to produce an expansion wave at or close to the leading edge of the auxiliary surface which will interact with the shock wave a short distance below the auxiliary airfoil thereby rendering the shock wave and sonic boom less severe at ground level.

The auxiliary surface may comprise a series of spaced-apart surfaces for producing a series of expansion waves for attenuating the principal shock wave as well as the shock waves produced from the auxiliary surfaces. Alternatively, the aforementioned modified aerodynamic structure may be employed as the primary airfoil.

These and other features of the present invention may be more fully appreciated when considered in the light of the following specification and drawings, in which:

FIG. 1 is a diagrammatic illustration of a supersonic aircraft embodying the present invention;

FIG. 2 is a diagrammatic illustration of a conventional wing in the form of a flat plate showing the relationship of the fluid source disturbance or shock wave resulting from an object travelling at supersonic speed;

FIG. 3 is a diagrammatic illustration showing the relationship of the shock wave and an expansion wave and the point of interaction relative to the wing-leading edge.

FIG. 4 is a diagrammatic illustration of an airfoil structure in the form of a flat plate illustrating the relationship and the point of coincidence of the shock wave and the expansion wave in the manner of FIG. 3;

FIG. 5 is a diagrammatic illustration of a lifting system in the form of flat plates showing the relationship of the conventional wing and the auxiliary surface embodying the invention and the resulting relationship of the shock and expansion waves and their point of interaction;

FIG. 6 is a diagrammatic illustration of the lifting system in accordance with the present invention illustrating the relative slopes of the primary and auxiliary surface relative to a characteristic line; and

FIG. 7 is a diagrammatic illustration of the primary and auxiliary surfaces in accordance with the present invention showing a modified auxiliary surface and the resulting wave interactions.

FIG. 8 is a diagrammatic illustration of another embodiment of the invention;

FIG. 9 is a diagrammatic representation of the signature for the embodiment of FIG. 3;

FIG. 10 is a diagrammatic illustration of the shock and expansion waves for a conventional aircraft constructed in accordance with the embodiment of FIG. 8; and

FIG. 11 is still another embodiment of the concept of FIG. 8.

The present invention will be described as it may be embodied in a supersonic aircraft. The aircraft is illustrated in FIG. 1 as a conventional supersonic aircraft 10. It should be understood that the only portion of the supersonic structure 10 that need be considered is the lifting and auxiliary surface geometry. The wing structure 11 may be of conventional design for operating at supersonic speeds. Accordingly, the shape of this surface 11 may be in accordance with conventional design. The aerodynamic object or aircraft 10 is provided with an auxiliary surface 12 mounted below the primary wing 11 in the fashion of a biplane. The auxiliary surface 12 is arranged and oriented relative to the primary wing to produce an expansion wave which interacts with the shock wave produced by the primary wing when the aircraft 10 is moving at supersonic speeds. The expansion wave created by the auxiliary airfoil 12 is developed at its lower surface 12 to interact with the shock wave from the primary wing 11 a short distance from the auxiliary surface 12 to attenuate the shock wave and thereby essentially eliminate the sonic boom for all practical purposes. It should be understood that the auxiliary surface 12 may be movably mounted to the aircraft to change its position relative to the primary airfoil 11 in accordance with presently known methods employed in supersonic aircraft design. The auxiliary surface I2 may be movable in accordance with the supersonic speed at which the aircraft I0 is moving to modify the point at which the expansion wave is being produced relative to the shock wave emanating from the primary airfoil or wing II.

The basic principle that must be kept in mind in the practice of the present invention is that when an object such as the aircraft I0 is moving at supersonic speeds, the flow of air beneath the primary wing 11 is caused to undergo a pressure increase in the form of a shock wave which manifests itself at ground level as a sonic boom when the aircraft is moving at supersonic speeds. Thus, the modifications of this sudden pressure increase (shock wave) by means of the auxiliary airfoil l2 causes a reduction in the magnitude of the pressure jump across the shock wave produced by the primary wing. The concepts or theory upon which the relationship of the airfoils 11 and 12 are based for reducing the sonic booms will now be considered.

The consideration of these concepts for the purposes of this disclosure will be in terms of aerodynamic surfaces in the form of flat plates. It will be recognized that those skilled in the art can adapt these concepts to conventional airfoil shapes for producing the same results.

When an object is in motion at a speed greater than the speed of sound in the surrounding fluid, the presence of the object is signalled along lines or surfaces, which radiate from the source of the disturbance in a direction of angle B (beta) relative to the local flow direction: See FIG. 2. For example, consider a flat plate AB, at an angle of attack, (1 (alpha) moving at a speed V in a fluid in which the speed of sound is C, all as shown in FIG. 2. The ratio V/C is conventionally called the Mach number and is defined at the local speed of the object relative to the fluid, divided by the local speed of sound in the fluid. The Mach number is a convenient numerical value for relating speeds to the speed of sound.

The direction of propagation B of a disturbance is called the characteristic direction and is determined only by the local Mach numberM."

It is important to note here that only very small disturbances propagate at the characteristic direction [3. Larger disturbances propagate in the direction 0 (theta) which is somewhat larger than B, as shown in FIG. 2.

Disturbances which deflect the fluid in a manner which cause an increase in local pressure (compressive), tend to coalesce into large, sudden changes and form shock waves (AC in FIG. 2) which propagate at the larger angle 0.

Expansive disturbances such as that at the upper surface of the flat plate (A-FG in FIG. 2) tend to fan out and create a region in which the pressure decreases gradually, thus their presence is signalled along the characteristic direction 3, to the local flow vector.

The properties (pressure, temperature, speed of sound) all change when the fluid crosses a shock wave (AC) or a characteristic (AF), of an expansion fan. In particular the properties, behind a shock wave change in a manner that causes the next expansion wave to have a leading characteristic which is at an angle (B a), which is larger than 0, when measured from the direction of motion. Thus, the expansion wave BDE, eventually overtakes and interacts with the shock wave AC, at a distance Li from the flat plate; See FIG. 3. I1 is then the vertical distance from the leading edge of the airfoil to the coincident point of the two waves.

Referring to FIG. 3, in particular, above point C, Y 111, the fluid properties, behind the shock wave and ahead of the expansion wave (region ABC) are constant. This implies that the pressure increment across the shock wave A p= 2p., is a constant everywhere from A to C, since the pressure ahead of the shock wave A-C is undisturbed and therefore constant. Beyond the point C, Y the pressure jump Ap, or shock intensity decreases, due to the interaction of the shock wave and the expansion wave.

The exact rate of decrease of Ap as a function of Y, cannot be predicted with great accuracy, but studies have indicated that a close approximation for this attenuation phenomenon is given by the following relationship:

3/4 (Amy for Y Y* tanB= (1) Thus the P m jump (Ap),, at a position Y is decreased from the initial value (A *at Y Y* by the ratio (Y*/Y) i or mathematically 5 In the simple case of a flat plate airfoil, as discussed above, ljand (A p)y* are determined by the flight Mach number, M, and the angle of attack a only. Thus for any value of Y,the value of (Ap)Y is determined by the value of Y*/Yand (Ap) Y as given by Equation 3 hereinabove.

We are concerned about the value of (A p)Y, at the ground, resulting from the overflight of an object or aircraft at supersonic speed. Thus Y is the altitude of the aircraft and from Equation 3 it is evident that the attenuation of the pressure jump depends upon the ratio Y or the ratio of If to flight altitude Y.

It is therefore beneficial to reduce If? to as small a value as possible so that for flight at an altitude I feet the value {*I Y would be as small as possible thus causing (A M to be as small as possible.

Reduction of (A p),,, the pressure jump across the shock wave at the ground would minimize the annoying and destructive effects resulting from the supersonic overflight of an aircraft. Thus, it is important to investigate the factors which affect the value of Iff.

Considering the same simple case of a flat plate airfoil A- B, the value of if can be determined from simple geometrical considerations, and is expressed in terms of 0, B 2, a and L as follows:

wherein L is the length or chord of the airfoil AB; See FIG. 4.

Since a, 0, B are determined by the aircraft weight (lift) and flight Mach number they are not subject to arbitrary modification for purpose of reduction of (A p)Y.

The purpose of this analysis is to describe a practical method for reduction of (A p) for a given aircraft, flying at a given altitude, at any given Mach number.

It appears from Equation 4 and the previous considerations, that a reduction of (A p),,, can be most readily achieved by reduction of IQ, and that this can most readily be accomplished by a reduction of the value of L.

In the case of a flat plate airfoil, L is the physical distance between leading and trailing edges of the plate, and cannot be arbitrarily reduced without a corresponding reduction of lift, which must necessarily be maintained equal to the weight of the aircraft. However, for purposes of estimating the value of X1 in Equation 4, L is the distance between the point of origin of the shock wave and the point of origin of the expansion fan.

The separation L of the shock wave and expansion fan can be reduced by the introduction of an auxiliary surface M-N, as shown in FIG. 5. The auxiliary surface MN is located and oriented in a manner such that its leading edge produces an expansion fan at its lower surface, which interacts and attenuates the shock wave AC from the primary airfoil. The distance between M and P, P being the point on the shock wave just in front of M, can now be reduced to a small value, by placing the auxiliary airfoil M-N in the location as shown in FIG. 5. Since the shock wave will have a slope which varies with flight Mach number and angle of attack it may be desirable to provide some method of adjustment for the location of the auxiliary surface M-N. However, since most of the flight path of supersonic aircraft will occur at cruising Mach number it may be feasible to design the auxiliary surface as a fixed surface for optimum performance at cruising speeds only.

As an example to illustrate the capability of an auxiliary surface in reduction of the magnitude of the sudden pressure jump, P)y of a shock wave at a distance Y greater than, I/ consider a case where the cord L of the primary wing is 50 feet. An auxiliary surface is installed so that the leading edge is one foot behind the shock wave. (MP=l .0 ft.) The pressure jump (A p) at any distance Y below the aircraft will be reduced to of the value it would have without the auxiliary wing. 5 In most practical design configurations, supersonic aircraft surfaces do not have point expansions such as that at the trailing edge of a flat plate, other design considerations dictate the desirability of surfaces with more gradual changes of slope. Thus, the expansion waves which occur behind the shock waves are in general derived from curved surfaces which gradually change slope from that of the leading edge towards a zero slope, parallel to the free stream direction. Expansions which are stretched out as compared to a point expansion, can always be shown to produce less rapid shock attenuation than a point expansion of the same strength, if the point expansion originates sufficiently close to the shock wave origin. For this reason it can be said that the use of an auxiliary airfoil of the type previously discussed will always produce large reductions in the shock intensity (A p) compared to the shock intensity resulting from a single airfoil of practical shape.

The auxiliary airfoil MN of FIG. 5 will always have its lower surface of lower slope than the slope of the lower surface of the primary airfoil AB, at the point on the same characteristic as the leading edge of the auxiliary airfoil M N; See FIG. 6. This will insure the presence of an expansion wave at the leading edge of the auxiliary airfoil MN as required to produce the rapid shock attenuation. To avoid difficulties of separation encountered at sharp expansion points, it may be necessary to provide a more gradual curvature at the expansion point of the auxiliary airfoil as shown in FIG. 7.

The upper surface of the auxiliary surface must be designed in a manner which prevents the introduction of undesirable forces such as negative lift or high drag or undesirable shock waves which might interfere with other components of the aircraft.

The concept of the present invention can also be implemented through the provision of an aerodynamic structure constructed and defined to produce a series of expansion waves at its lower surface. The generation of the expansion waves is accompanied by the generation of shock waves from such a surface and the expansion waves are generated to attenuate a leading shock wave from an adjacent surface. Such an airfoil structure may be added to a conventional supersonic aircraft or may be employed as the primary wing for the aircraft. The implementation of this method and apparatus is disclosed in conjunction with FIGS. 8-l 1.

It has been shown that the pressure rise due to the passage of a shock wave is related to the intensity of the shock wave at its origin reduced by a factor depending upon the distance of the point of observation from the shock wave origin where L is the distance between the shock wave origin and the expansion wave origin at Y=o. For airfoils of the same :geometry and at the same flight conditions (Mach Number and angle of attack) X: is directly proportional to L.

Therefore, if we consider two lifting systems, one having a chord C and the other having N airfoils each having a chord C/N, the series of N airfoils will have a shock intensity reduced" by the factor v V gs cgn pared to that of the sir gle airf oil as indicated in FIGS.

providing the flight Mach Numbers and angles of attack are all the same.

In this configuration of the series of airfoils illustrated in FIG. 8 the shock waves produced at the leading edge of an airfoil is attenuated by the expansion wave produced at a point spaced from but adjacent the leading edge of the same airfoil; See FIG. 8. The series of airfoils 1, 2, 3 and 4 are arranged on the aircraft 10 so that each of them is at the angle of attack of an (alpha) and the sum of their chords equals C. They are further illustrated by the trailing edge of one airfoil being in alignment with the leading edge of the next following airfoil. This series of airfoils can be employed as the primary wing for a conventional supersonic aircraft in which case the elemental airfoils are shaped and oriented relative to the vehicle proper to have the proper lift and aerodynamic properties alternatively, the conventional supersonic aircraft 10 can be modified through the substitution of the aforementioned series of airfoils shown in FIG. 8 for the auxiliary surface 12 of FIG. I. The primary shock wave produced by the primary airfoil will interact with the expansion wave produced at the leading airfoil or airfoil l in FIG. 8. The interaction of the shock and expansion waves for such a configuration is best appreciated from examining FIG. 10.

lated as follows A configuration which shows the same advantage in reducing the sonic boom but provides a more practical structural design configuration is shown in FIG. 11.

In the configuration of FIG. 11 the lifting surface is comprised of a single rigid unit while still retaining the advantage of the series of airfoils of FIG. 8 for producing closely spaced shock waves and expansion waves to produce lower shock wave intensities and therefore less sonic boom annoyance at the ground.

It should now be appreciated that the present invention has advanced the state of the aircraft art through the methods and apparatus for reducing sonic booms by the simple structures for diverting airflow to produce an expansion wave for interacting with the shock wave.

It is further understood that the surfaces introduced for shock attenuation and reduction of sonic boom effects, may 7 alter the lift, drag and lift/drag ratio of the aircraft. Depending upon the geometry of these surfaces, the aircraft performance may be either improved or impaired. Therefore, care must be exercised in the geometrical shape and location of these surfaces' What is claimed is:

l. A method of reducing sonic booms created by objects moving in fluids at speeds greater than the speed of sound, the object having a primary surface or wing with local pressures greater than ambient on its lower side leading to the formation of shock waves traveling towards the ground and thereby sonic booms at ground level when the object is traveling at supersonic speeds,

including the steps of:

I 55 providing an auxiliary airfoil below the primary surface having a lower surface of a lower slope than the slope of the lower surface of the primary surface,

positioning the auxiliary airfoil so that it does not interfere with the travel of the shock wave towards the ground, and causing the auxiliary airfoil to divert the airflow from adjacent the primary airfoil to produce an expansion wave traveling towards the ground for interacting with the shock wave in its unimpeded travel toward the ground at a distance spaced from the moving object and thereby cause it to be attenuated.

2. In an aerodynamic vehicle capable of traveling at speeds greater than the speed of sound, the vehicle having a primary wing, the airflow beneath the primary wing assuming a parallel relationship therewith and causing increases in local pressures leading to the formation of shock waves that travel towards the ground and thereby sonic booms when the object is traveling at supersonic speeds, the improvement comprising,

an auxiliary surface mounted below the primary wing in a nonparallel relationship and having a lower surface of lower slope than the slope of the lower surface of the primary wing for diverting the airflow from a parallel rela tionship with said primary wing surface and positioned to produce an expansion wave traveling towards the ground at or close to its leading edge that will interact with the shock wave a short distance'below the auxiliary surface while permitting the shock wave to proceed toward the ground without interference by a solid surface.

3. In an aerodynamic structure as defined in claim 2 wherein the auxiliary surface is movably secured to the structure for changing the position of the leading edge relative to the shock waves.

4. In an aerodynamic vehicle as.defined in claim 2 wherein the auxiliary surface is arranged partially underneath the primary wing and extending rearwardly thereof, the auxiliary surface being oriented so that its leading edge produces an expansion wave at its lower surface for attenuating the shock wave produced at the primary wing, the interaction being produced in a short distance from the vehicle thereby rendering it tolerable at ground level.

5. in an aerodynamic structure as defined in claim 4 wherein the auxiliary surface has a slope lower than the primary wing for insuring the production of the expansion wave at or near the leading edge of the auxiliary surface thereby producing rapid shock attenuation.

6. in an aerodynamic vehicle capable of travelling at speeds greater than the speed of sound, as defined in claim 2 wherein the auxiliary surface comprises a plurality of spaced-apart auxiliary surfaces arranged on the vehicle in serial fashion for diverting the airflow from a parallel relationship with the said wing surface to produce an expansion wave at a predetermined distance from its leading edge, and a shock wave adjacent the leading edge, the arrangement of said auxiliary surfaces being such that the leading auxiliary surface produces an expansion wave that will interact with the shock wave a short distance below the auxiliary surface and the successive auxiliary surfaces produce an expansion wave that will interact with any shock wave produced at the trailing edge of said auxiliary surface.

7. In an aerodynamic vehicle capable of traveling at speeds greater than the speed of sound including a wing comprising a plurality of spaced-apart airfoils mounted to the vehicle in serial chordwise fashion for diverting the airflow positioned to produce an expansion wave spaced adjacent to the leading edge of each of said surfaces and traveling towards the ground, the arrangement of said surfaces being further characterized by the formation of shock waves at or adjacent their leading edges and traveling towards the ground whereby the shock wave produced at a leading edge is permitted to travel toward the ground without interference by a solid surface until it interacts with the expansion wave from the said surfaces a short distance below said surfaces and in its travel towards the ground thereby rendering the shock wave tolerable at ground level. 8. In an aerodynamic vehicle capable of traveling at speeds greater than the speed of sound including a wing of unitary construction having a lower surface constructed and defined with a series of surfaces positioned for producing expansion waves for diverting the airflow to produce an expansion wave spaced adjacent to the leading edge of each of said surfaces and traveling towards the ground, the arrangement of said surfaces being further characterized by the formation of shock waves at or adacent their leading edges and traveling toward the ground whereby the shock wave produced at a leading edge is permitted to travel toward the ground without interference by a solid surface until it interacts with the expansionwave from the said surfaces a short distance below said surfaces and in its travel toward the ground thereby rendering the shock wave tolerable at ground level.

' UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 ,647, 160 Dated March 7, 1972 Inv n Morton Alperin It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, line 62, "C, Y should read --C,Y 7 Y*- (Application page 7, line 19 Column 4, line 6, "(Ap)y*" should read A p)Y*-- (Application page 8, line 2) Column 5, line 60, "Y" should read --Y*--(application page 11,

line 30 Signed and sealed this I 8th day of July 1972.

( SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSOHALK Attesting Officer Commissioner of Patents 

1. A method of reducing sonic booms created by objects moving in fluids at speeds greater than the speed of sound, the object having a primary surface or wing with local pressures greater than ambient on its lower side leading to the formation of shock waves traveling towards the ground and thereby sonic booms at ground level when the object is traveling at supersonic speeds, including the steps of: providing an auxiliary airfoil below the primary surface having a lower surface of a lower slope than the slope of the lower surface of the primary surface, positioning the auxiliary airfoil so that it does not interfere with the travel of the shock wave towards the ground, and causing the auxiliary airfoil to divert the airflow from adjacent the primary airfoil to produce an expansion wave traveling towards the ground for interacting with the shock wave in its unimpeded travel toward the ground at a distance spaced from the moving object and thereby cause it to be attenuated.
 2. In an aerodynamic vehicle capable of traveling at speeds greater than the speed of sound, the vehicle having a primary wing, the airflow beneath the primary wing assuming a parallel relationship therewith and causing increases in local pressures leading to the formation of shock waves that travel towards the ground and thereby sonic booms when the object is traveling at supersonic speeds, the improvement comprising, an auxiliary surface mounted below the primary wing in a nonparallel relationship and having a lower surface of lower slope than the slope of the lower surface of the primary wing for diverting the airflow from a parallel relationship with said primary wing surface and positioned to produce an expansion wave traveling towards the ground at or close to its leading edge that will interact with the shock wave a short distance below the auxiliary surface while permitting the shock wave to proceed toward the ground without interference by a solid surface.
 3. In an aerodynamic structure as defined in claim 2 wherein the auxiliary surface is movably secured to the structure for changing the position of the leading edge relative to the shock waves.
 4. In an aerodynamic vehicle as defined in claim 2 wherein the auxiliary surface is arranged partially underneath the primary wing and extending rearwardly thereof, the auxiliary surface being oriented so that its leading edge produces an expansion wave at its lower surface for attenuating the shock wave produced at the primary wing, the interaction being produced in a short distance from the vehicle thereby rendering it tolerable at ground level.
 5. In an aerodynamic structure as defined in claim 4 wherein the auxiliary surface has a slope lower than the primary wing for insuring the production of the expansion wave at or near the leading edge of the auxiliary surface thereby producing rapid shock attenuation.
 6. In an aerodynamic vehicle capable of travelling at speeds greater than the speed of sound, as defined in claim 2 wherein the auxiliary surface comprises a plurality of spaced-apart auxiliary surfaces arranged on the vehicle in serial fashion for diverting the airflow from a parallel relationship with the said wing surface to produce an expansion wave at a predetermined distance from its leading edge, and a shock wave adjacent the leading edge, the arrangement of said auxiliary surfaces being such that the leading auxiliary surface produces an expansion wave that will interact with the shock wave a short distance below the auxiliary surface and the successive auxiliary surfaces produce an expansion wave that will interact with any shock wave produced at the trailing edge of said auxiliary surface.
 7. In an aerodynamic vehicle capable of traveling at speeds greater than the speed of sound including A wing comprising a plurality of spaced-apart airfoils mounted to the vehicle in serial chordwise fashion for diverting the airflow positioned to produce an expansion wave spaced adjacent to the leading edge of each of said surfaces and traveling towards the ground, the arrangement of said surfaces being further characterized by the formation of shock waves at or adjacent their leading edges and traveling towards the ground whereby the shock wave produced at a leading edge is permitted to travel toward the ground without interference by a solid surface until it interacts with the expansion wave from the said surfaces a short distance below said surfaces and in its travel towards the ground thereby rendering the shock wave tolerable at ground level.
 8. In an aerodynamic vehicle capable of traveling at speeds greater than the speed of sound including a wing of unitary construction having a lower surface constructed and defined with a series of surfaces positioned for producing expansion waves for diverting the airflow to produce an expansion wave spaced adjacent to the leading edge of each of said surfaces and traveling towards the ground, the arrangement of said surfaces being further characterized by the formation of shock waves at or adjacent their leading edges and traveling toward the ground whereby the shock wave produced at a leading edge is permitted to travel toward the ground without interference by a solid surface until it interacts with the expansion wave from the said surfaces a short distance below said surfaces and in its travel toward the ground thereby rendering the shock wave tolerable at ground level. 